PROJECT SUMMARY (See insti-uctions): Most neurodegenerative diseases, including Alzheimer's disease (AD), are disorders of protein aggregation in which specific proteins that are normally soluble, aggregate in the intra or extracellular space of the brain. In AD, a key factor that regulates whether an aggregation prone protein goes on to misfold is its concentration. Studies have shown that synaptic activity due to both presynaptic arid postsynaptic factors is coupled with the neuronal release of amyloid-B (AB). This suggests that understanding how integrated synaptic and network activity regulate both AB and potentially other proteins involved in neurodegenerative disease, may provide novel insights into pathogenesis. We found that in the brain interstitial fluid of mice (ISF), AP levels are dynamically and positively associated with the number of minutes awake per hour. Pharmacological studies showed that exogenous and endogenous orexin modulates both wakefulness and AB levels. Chronic sleep deprivation markedly increased and an orexin-receptor antagonist decreased AB deposition in APP Tg mouse models. Our preliminary data show that in ISF AB levels as well as measures of brain metabolic/synaptic activity predict how much AB deposition will occur in specific brain regions. Based on these results, we hypothesize that differences in brain metabolic/synaptic activity between brain regions regulate ISF AB levels and that the sleep/wake state regulates both soluble AB levels and ultimately AB deposition via effects on synaptic activity. The specific aims are: 1) To dynamically measure the levels of ISF AB, molecules linked with synaptic activity such as lactate, molecules controlling wakefulness (orexin), and sleep (growth hormone releasing hormone-GHRH) by in vivo microdialysis in different brain regions with aging. 2) To determine the effects of genetic and pharmacological manipulation of orexin and GHRH signaling as well as effects of endogenous NMDA receptor activation, ERK signaling, and LRP1 on ISF AB fluctuations and the sleep/wake cycle in collaboration with projects 2 and 3. 3) To determine the relationship between mean sleep/wake time, other sleep features, and AD biomarkers (amyloid imaging, CSF AB and tau) in an ongoing study of cognitively normal humans (the adult children study) 45-75 years of age.